Our studies on the chemistry of troponin will be continued. Specifically we would like to be able to itemize the series of events which occur on the binding of Ca2 ion. One way to approch this problem, is to prepare biologically active fractions from the troponin subunits. This can be done by selective cleavage of the polypeptide chain, for example at the cysteine or methionine residues. If smaller fragments can be prepared in an active form then the process of resolving the mechanism of action of troponin should be simplified. Important data on the site of interaction for the subunits should also be obtained from this study. The regulatory mechanism in smooth muscle is also being studied. So far we have not been able to identify in the smooth muscle actomyosin any components similar to skeletal muscle troponin. By a series of dfferent techniques we are attempting to isolate the smooth muscle regulator proteins and preliminary evidence indicates that one or two proteins of molecular weight approximately 100,000 are functional in this regard. There are many other differences between smooth and skeletal muscle and we have therefore commenced a program to study a wider field of smooth muscle biochemistry.